1. Field of the Invention
The present invention relates to a rotating electric apparatus such as a motor or generator, and a method for connecting stator coils thereof.
2. Description of the Related Art
The types of stator windings are generally classified into a concentrated winding arrangement and a distributed winding arrangement; in the former, coils are concentrated per magnetic pole tooth, and in the latter, coils are provided across a plurality of slots so that different-phase or same-phase coils are made to overlap one another at a coil end position. In the concentrated winding arrangement, although a small coil end of a stator can be provided which is advantageous for reduction in size and enhancement in performance of a rotating electric apparatus, a rotating magnetic field produced on the inner circumference of the stator is not evenly distributed, thereby bringing about a disadvantage that noise is prone to occur due to harmonics. By way of contrast, in the distributed winding arrangement adopted for a stator in conventional practice, it is generally possible to restrict a rotating magnetic field produced on the inner circumference of the stator within a substantially sinusoidal range for reducing noise to a lower level than that in the concentrated winding arrangement. However, in the distributed winding arrangement, since there is a significant extent of overlapping of coils at a coil end position, the volume of the stator is larger than that of the concentrated winding arrangement, giving rise to difficulty in size reduction and performance enhancement of a rotating electric apparatus.
For example, in the design of a main drive motor for an electric automobile, it is required to provide a high output by using a limited battery voltage under a considerably restricted condition on availability in mounting space. As a means for meeting requirements for extremely severe levels of compactness and high output, there is known a technique of increasing a coil space factor in a stator slot by using a copper element wire having a substantially rectangular cross section as a coil wire material. In a concentrated winding type of stator, a copper element wire having a substantially rectangular cross section is applicable relatively with ease since the configuration of each coil is rather simple. Earlier patent disclosures dealing with embodiments in which stator coils are structured in a concentrated winding form by continuously providing a copper element wire having a substantially rectangular cross section are found in patent documents 1 and 2 indicated below.
In cases where a copper element wire having a substantially rectangular cross section is used for each stator coil in a distributed winding form, it is required to circumvent possible occurrence of mutual interference on element wires while keeping the element wires in a proper alignment. As a conventional means for meeting this requirement, there is known a technique of providing a three-phase coil arrangement in a concentric winding form as disclosed in patent document 3 indicated below. In the coil end structure of the three-phase coil arrangement, U-phase, V-phase and W-phase members are stacked on one another axially without overlapping thereof, thereby preventing mutual interference on the members of three different phases.    Patent document 1: Japanese Unexamined Patent Publication No. 2004-80860    Patent document 2: Japanese Unexamined Patent Publication No. 2006-288123    Patent document 3: Japanese Unexamined Patent Publication No. 2006-101654
However, since the members of the three phases have different coil end configurations to prevent mutual interference on the element wires stacked at a coil end position, there is an inevitable disadvantage that the size of the entire coil end is rather large.
It is to be noted that the following aspects of the present invention concerning the problems to be solved by the present invention are also applicable to resolution of other problems that are critical in product manufacturing as will be described later.